Embodiments of the present invention generally relate to desalination and purification and more particularly to liquid purification through evaporation and condensation assisted by solar energy.
Desalination systems are systems that remove sugar or other dissolved solids from water, most often to produce potable water. Currently, several methods of desalination are employed by commercial desalination systems, the most popular being reverse osmosis and flash vaporization. Both of these methods are relatively expensive, have large energy requirements and certain components that wear out frequently. For example, reverse osmosis systems force water through membranes and these membranes, which are expensive in and of themselves, could become clogged and torn, thus necessitating frequent replacement. Similarly, flash vaporization systems have corrosion and erosion problems due to the spraying of hot brine within these systems. The energy requirements for a reverse osmosis system may be approximately 6 kWh of electricity per cubic meter, of water, while a flash vaporization system may require as much as 200 kWh per cubic meter of water. Due to the high energy inputs, frequent maintenance, and associated costs desalination of water on a large scale basis has been relatively expensive, often more expensive than finding alternate sources of groundwater. These same factors have made desalination using these methods on a small scale unfeasible.
Solar energy can be harnessed for desalination either directly or indirectly. Collection systems, which use solar energy to produce distillate directly in the solar collector, are called direct collection systems, whereas systems that combine solar energy collection systems with conventional desalination systems are called indirect systems. In indirect systems, solar energy is used to either generate the heat required for desalination or generate electricity subsequently used to provide electric power for conventional desalination plants such as multi-effect, multi-stage flash or reverse osmosis systems as mentioned above.
Direct solar desalination although suited for very small production systems, such as solar stills, suffer from a very low production rate caused by a low operating temperature and near atmospheric pressure of a resulting steam. Solar stills use exactly the same processes, which in nature generate rainfall, namely evaporation and condensation: a transparent cover encloses a pan of saline water that is first evaporated by the trapped solar energy within the enclosure and then condensed on the inner face of the sloping transparent cover. This distilled water is generally potable; the quality of the distillate is very high because all the salts, inorganic and organic components, and microbes are left behind in the bath. One of the problems that negatively influence the still performance is the direct contact between the collector and the saline water, which may lead to corrosion and scaling in the still. The biggest issue for the solar stills however are their rather low efficiency and water production rate: a typical production rate of a solar still is about 4 L/m2/day or less.
Accordingly, a need exists for a desalination and or purification devices that are suitable for a small scale operation that is low cost and reliable.